Suspension is as old as wheeled vehicles, and some higher priced buckboard wagons had seats mounted on leaf springs to prevent the driver and passengers from having sore backs (Figure 1). Any part of a vehicle that is being carried by the springs is sprung weight (like the seat on the wagon). And anything not being carried by the springs is un-sprung weight (like the rest of the wagon). Un-sprung weight on a vehicle would be the lower control arms, axles and the tire and wheel assemblies.
Most vehicles have steel springs, but some have air suspension rather than the metal springs (Figure 2). Air suspension requires electronics, piping, a pump and a height sensor. Air suspension systems tend to be problematic on high mileage vehicles and there are kits for sale to replace the air springs with coils.
Leaf springs are usually on the rear of pickup trucks and since leaf springs change shape (getting longer as they’re compressed), one end of a leaf spring will have a hinged portion that allows the springs to lengthen and shorten as the vehicle is loaded and unloaded (Figure 3). Any spring can break, and springs can be dangerous. So be careful.
Four-wheel drive vehicles usually have torsion bars because the axles driving the front wheels pass through the place where the springs would normally be (Figure 4). Torsion bars are thick spring-steel rods designed to twist when the vehicle is loaded and reverse that twist when there’s less loading. This provides suspension support. Torsion bars are six-sided (like the head of a bolt) on each end with the front end inserted in a six-sided matching hole, located in the front control arm. The rear end of the bar is inserted in a heavy, wrench-like lever with a six-sided hole. That lever sits on a heavy bolt so it can be adjusted.
The cool thing about torsion bars is that they’re easily adjustable (Figure 5). To determine adjustment, measure ride height from the bottom of the wheel to the fender well. Remember to mark the bars whenever they have to be removed. And make sure to put them back exactly as they were — left and right are NOT interchangeable. Also, make sure you know the front from the rear on each bar. Reinstalling torsion bars the wrong way (backward, or on the wrong side of the vehicle) ruins the ride quality of the vehicle (GM and some other manufacturers will put L and R marks and arrows on the ends of their torsion bars).
Shock absorbers
Since springs tend to keep on bouncing after their cushioning action, shock absorbers — dampers, as it were — became the order of things early on. A traditional shock absorber is mounted almost vertical, with a polished plunging shaft bolted to the frame, and that shaft slides vertically through a seal into a pressurized chamber. On the bottom end of the shaft, there is an attached plate that slides in a sealed tube. The tube is bolted to the lower control arm, which moves in response to bumps, dips, cornering, etc.
The plate affixed to the shaft has a seal, where it slides in the tube and has small holes in it. This is the heart of the shock/damper. When shock absorber action is happening, the polished shaft (connected to the frame) slides in to shove the plate down within its polished tube (which, by the way, is partially filled with oil) (Figure 6). The action of the suspension spring strives to return the rod (and its plate) to their original position. This usually overshoots a bit and is why damping happens. The oil in the shock tube is forced to make its “sluggish” way through the holes as the plate reciprocates. This action effectively stops the vehicle from bouncing after going over a bump (or through a dip) and prevents the wheels from beginning a resonant bouncing that leads to worn tires. Some vehicles have small, shock-like steering dampers mounted laterally and connected to the steering mechanism. This prevents front wheel shimmy. Old VW beetles had these, as do many four-wheel-drive vehicles.
Variably damping shocks on some performance vehicles have an electronic mechanism that adjusts instantly to restrict the oil flow through the plate holes. This stiffens the suspension when cornering, panic-stopping or when the customer selects “firm” with a switch on the dash. There are several ways this variable damping can be done, but most shocks don’t work that way.
Just about all newer shock absorbers are nitrogen gas-charged, along with the oil, and provide some support for vehicle weight in addition to their dampening function. They come “loaded” and must be “unloaded” before installation. You either turn the polish rod or remove a strap. They want to remain extended when at rest and will try to. Older shocks didn’t work this way. If you shoved one halfway down, it’d stay there. On an aging shock absorber (or one that has been damaged), the oil will begin to leak out. Usually, we catch the oil leaking out of the shock when we have it on the lift and see a wet shock housing. If the shocks leak enough of their oil, the car will develop a noticeable bounce while driving, because the damping effect of the shock absorbers has been lost. It’s best to replace shocks in pairs. Some shocks are easily replaced, and others are surprisingly difficult. When you’re handling a worn-out shock, you can compress and extend it easily with your hands. New shocks are very stiff and are practically impossible to manipulate by hand if you’re not a He-Man.
Struts
My dad ran a VW shop for 30 years, and when VW came out with their Super Beetle in 1972, he expressed a dislike for the new bug because, in his words: “They have a Mickey Mouse front end under them.” Dad was referring to MacPherson Strut front suspension, which eventually found its way to the rear.
Rather than a coil spring (riding between a frame-welded truss and a lower control arm), the stamped steel body of the vehicle has an upside-down reinforced well or “bucket” (I call it a strut tower). It nearly goes to the underside of the hood, and that’s where the strut carries the sprung weight. This makes the vehicle’s center of gravity a lot lower, giving it a lot more stability during turns and evasive maneuvers (Figure 7). Struts are a shock and a spring assembled as a unit. The struts are available as an assembled unit (that’s the smartest way), or in two pieces. By using a special heavy-duty spring squeezer, the strut can be replaced, independent from the spring. But, be careful — that spring is strong enough to take your head off.
On vehicles where the strut provides the steering axis, there is a special bearing at the top of the strut unit that enables the strut to turn (with the wheels) while it carries the weight of the vehicle. These bearings are of varying designs and can wear out or dry out so that the customer hears funky noises while turning. If the bearing is the problem, the noise will be consistent while turning the wheels and can be felt with your hand. If you kneel by the tire and put your fingers on the spring while the wheels are turned with the car sitting still, the wear will be evident.
This steering-axis type strut suspension doesn’t have an upper ball joint or an upper control arm. It just has a lower control arm and a ball joint. The bottom of the strut is attached to the steering knuckle and plays an important part in vehicle alignment adjustments. They are available with either eccentric bolts (where the strut attaches to the knuckle for camber adjustments) or camber may be adjusted by slotting the mounting holes in the strut tower and moving the upper part of the strut housing in the top of the tower, for caster and camber adjustments. This style can be a pain with a capital “P.”
Hondas and some other vehicles — including early Ford Fusions — have both upper and lower control arms with ball joints but still have strut suspension. On these, the strut assembly is attached to the lower control arm (just inboard of the lower ball joint), using what I like to call a “wishbone.” The upper part of the strut assembly is bolted high in the car’s body (like a conventional strut) but without the bearing. The steering axis on this kind of suspension passes through the upper and lower ball joints, rather than through the center of the strut.
Short story — working at the VW dealer back in 1983, I encountered a Rabbit with a rattling noise when going over bumps. It was coming from the left-rear strut. I removed and disassembled the strut (which was very easy) and checked everything, finding no witness marks or any reason for the rattle. I reassembled it and reinstalled it, but it still rattled going over bumps. Finally, I had Sam (the parts guy) order me all the composite pieces to build a new replacement strut and that took care of the rattle. I have no idea what was going on with the original strut.
Alignment issues
Aside from old-school Short-Long-Arm (SLA) suspension vehicles, weak front-springs sometimes need replacing to restore in-spec camber setting. But you need to make sure you get the right ones for the vehicle. Some pickups (for example) may have three different spring sizes, and using the wrong springs can cause ride issues. I found that out the hard way, working on a Dodge truck.
Alignments are, on most vehicles, a four-wheel affair nowadays. But the adjustments on newer-model cars are getting more sensible. The eccentrics for front caster and camber on a growing number of vehicles have been moved to the lower control arms, where it’s very easy to do. Fiddling with control arm shims (typical, on older vehicles) to set caster and camber was a drag, unless you were accustomed to it.
The toe alignment on the rear wheels is typically done with eccentrics, but sometimes the rear toe adjustments will be done with adjustment sleeves (like the front tie rods), which is a lot better. That being said, adjustment eccentrics in the rear (particularly in high-salt areas) can become so rusty and seized that the adjustments become impossible without doing some torch-work. There’s nothing like going into (what you think will be) a simple alignment only to have it turn into a monster.
Sway bar links
No suspension run-down would be complete without a discussion of sway bars. I found out just how necessary this component is when (as a teenager) I took a ’58 VW my dad had traded for, shoved an engine in it, and took it for a drive on a nearby dirt road. It was an awful ride; when I swerved right the body would sway sluggishly to the left and vice versa. It was dreadfully disappointing how bad this bug handled, and I had not experienced this before. When I drove back up to Dad’s shop, I told him how awful it was. I then asked what could be done about it. He explained that the ’58 VW was built without a sway bar — only I had no idea what a sway bar was at the time. The sway bar was part of the front axle assembly (on bugs that came with it).
“Take the front axle assembly off that ’64 model bug,” he told me, pointing at a vehicle in his boneyard “and put it on the ’58.” When I did that (no small feat for a 15-year-old), I was shocked at how much better that ’58 bug handled doing slalom drift runs on the dirt road. It now handled like a Porsche. No vehicle since the early ’60s (that I know about) has been built without at least one sway bar. These are so effective and so important to vehicle handling that many SUVs started including rear sway bars over 20 years ago to help prevent rollover.
A sway bar is a piece of spring steel that is clamped to the frame (in rubber grommets) with steel straps, and at each end of this crooked piece of steel there is a sway bar link attaching it to the lower control arm. When the vehicle corners, the sway bar acts in such a way that (since it is attached to both control arms) it keeps the car’s body from tilting as much.
Sway bar links are probably some of the cheapest components you can buy, and they need replacing on higher mileage cars when their rubber wears out and they begin to make popping sounds. It’s a good upsell to have a look at them and typically easy money when it comes to replacing them. But make sure you know how to stack the washers, bushings and spacers when installing them — newbies can find a lot of ways to do it wrong. Replacing sway bar links doesn’t require additional tasks like alignment adjustments and it’s fairly easy to do.
Sudden failures
There’s nothing more unsettling than the front-end or suspension parts (the really important ones) that die without warning “catastrophically.” When I was doing fleet maintenance down on the Texas coast, in the late ’70s, we transitioned from mid-70s Chevy pickups to late-70s Dodge pickups. That very rapidly racked up some pretty serious (and grueling) miles. We had half-hour lunches and we shop guys would sometimes make that mile-long run to Sabine Pass to have lunch at one of the cafes at the intersection. The road to town was rough and bumpy, and we drove one of the Dodge pickups down there and back — a cab full of happy-go-lucky guys.
When we got back, the guy who greased the cranes took that same truck out on the dockyard for the rest of the day to do his work. In the evening, when he was pulling the ’78 Dodge back into the shop, the left-lower ball joint broke and the bumper of that truck hit the floor like ton of bricks. It sounded like a bomb going off.
The next day we jacked the truck up, right there where it was parked, to replace that ball joint and saw (from the bi-color cross-section), looking at the “break,” that the ball joint had been cracked about halfway through for a pretty good while, before it finally broke. If that failure had happened during our 60-mph drive to the café earlier that day, I probably wouldn’t be sitting here typing these words right now. The ball port of the joint wasn’t worn, either, and the boot was still intact. It was a stealth failure that could have been fatal. A sister-truck to that one (another ’78 Dodge) had a tie rod end separate at highway speed. I was following the truck, and I had noticed that the right front wheel started whipping back and forth like a shopping-cart caster. I was behind the truck when it happened, and that truck crossed the oncoming lane and onto the shoulder. It then crossed that lane again and finally came to a stop on the right side of the road, about three feet off the shoulder. I’ve seen ball joints and tie rod ends fail on other vehicles, too — a ball joint on a 2001 F150 and a tie rod end on a 1987 F250, but both of those happened at very slow speeds. Ball joints usually fail while turning.
Finally, it bears mentioning that some shops will try to sell customers hundreds of dollars’ worth of front-end work that isn’t even necessary. As a second-opinion guy, I saw it repeatedly when I was instructing. A friend of mine who owns a tire shop told me he gets vehicles in for second opinions just about every week with the same circumstances. This shop or that one would try to fear-monger the customer into letting them replace all the ball joints and tie rod ends. When they came for a second opinion I couldn’t find so much as a busted boot anywhere, and all the joints would be tight and safe. Let me conclude by saying that there’s plenty of suspension work out there that needs doing, without trying to sell work that isn’t needed. Just a thought.
